Ceramics have many compelling properties that render them attractive candidates for dental restorations: these properties including hardness, chemical durability, wear resistance, and, in specific cases, machinability. The objective of this project in the broader Machinable Ceramics Program is to investigate the fracture and fatigue characteristics of dental ceramics, with an emphasis on machinable ceramics. We propose a systematic contact fatigue study using a novel and simple, yet powerful, Hertzian indentation methodology developed at NIST. Our emphasis will be on interrelations between damage accumulation in cyclic loading and key elements of material microstructure. A key element in the study will be the relationship between damage patterns with observations from clinical failures. Specific aims include: (1) carry out repeat-load indentation experiments on chosen machinable ceramics, to evaluate fatigue properties; (2) a systematic analysis of the damage mechanisms in these ceramics, using optical and electron microscopy and acoustic emission; (3) theoretically analyze the damage accumulation patterns, using fracture mechanics; (4) measure the strength of specimens as a function of number of indentation cycles, to assess lifetime characteristics; (5) conduct comparative tests in various environments, inert (dry nitrogen), air and water, to evaluate the effect of chemical enhancement in the damage process; (6) conduct comparative tests on machined and surface-modified surfaces, to investigate potential enhancement or inhibition of fatigue degradation from persistent surface stresses and flaw state; (7) correlate damage patterns on the laboratory specimens with those on clinical restorations (8) relate the observed properties to microstructural variables, so that materials processing strategies for the next generation of dental materials may be laid down. The techniques that we propose to use here to analyze the fatigue and fracture properties, based as they are on the most recent developments in fracture mechanics at the microstructural level, are at the forefront of current ceramics science. They offer a sound basis for the future materials evaluation and design for specific dental (and potentially other biomedical) applications. They also promise new insights into the machinability and wear resistance characteristics that form the focus of other phases of the broader program.